1. Field of the Invention
The present invention relates to infrared and optical systems. More specifically, the present invention relates to systems and methods for effecting steering of infrared and optical beams.
2. Description of the Related Art
For many applications, there is a need to generate images optically. Military and commercial aircraft applications, for example, utilize systems which transmit and/or receive infrared, near-infrared, optical or other electromagnetic energy. The input and/or output beams must be steered in a desired pointing direction.
For beam steering, the prior art includes steering mirrors, pointing gimbals and monochromatic electro-optical, beam steering mechanisms. Steering mirrors require output windows many times the size of the system optical entrance pupil to scan over a large field of regard. Unfortunately, the mirror form factor requirements greatly increase the size of the sensor package.
The gimbaled approach involves use of an imaging system mounted in a dome that is gimbaled to provide a desired pointing angle. The gimbals must point the entire sensor to scan the field-of-regard. Unfortunately, for aircraft applications, this requires a mirror below the platform line, which necessitates a hole in the platform. In addition, the dome and optical assembly is bulky, typically requires considerable volume, and has a radar cross-section which tends to increases the observe-ability of the vehicle.
The monochromatic electro-optical, beam steering approach involves the use of a liquid crystal as the manipulated medium. This approach relies on a diffractive grating pattern in a liquid crystal array. Displacing the grating causes a phase delay that steers the beam. Unfortunately this approach only operates effectively for monochromatic or near-monochromatic light sources. For non-monochromatic light sources, this approach causes undesirable color dispersion.
Accordingly, a need exists in the art for small, compact optical scanning system with small aperture size requirements, wide field-of-regard and minimal color dispersion characteristics.
The need in the art is addressed by the beam steering system and method of the present invention. The invention provides a means for optical beam steering over a broad spectral band and over a wide field-of-regard in a small, compact optical scanning system with small aperture size requirements, wide field-of-regard and minimal color dispersion characteristics.
The inventive system includes a novel device for receiving an input wavefront of electromagnetic energy along a first axis and for refracting the input wavefront as an output wavefront along a second axis. The device is a unique form of a liquid crystal array which can be electrically manipulated to change the effective refractive index of each pixel. The index of refraction of the device varies in response to an applied voltage. The voltage is supplied by a microprocessor and/or a servo-control system. By changing the index, the incident phase front can be steered at an angle with respect to the first axis and otherwise manipulated according to the index variant pattern induced in the array. Accordingly, the output beam is steered in response to the applied voltage.
In the illustrative implementation, the device is an array of liquid crystal devices. Counter-rotating optical wedges are provided for restoring color balance to the output wavefront. In the illustrative embodiment, a mirror is included for compensating the wavefront output by said first and second counter-rotating optical wedges. The wavefront reflected by the mirror may be output by an imaging lens or other suitable device.
In accordance with the present teachings, beam steering is accomplished through a refractive variation not a diffractive one. This allows the spectral bandwidth to be much broader than for a diffractively manipulated phase wavefront.